Light-emitting diode structure having progressive work function layer

Abstract

The present invention relates to an LED structure having a progressive work function layer, which adopts a conversion layer with a gradually varying work function as the medium for forming an Ohmic contact between the p-type GaN and the metal reflection layer. The work function of the conversion layer is not a single value. Instead, different quantities of dopants are doped at different depths of the conversion layer. Thereby, the conversion layer can match excellently the connected p-type GaN and the metal reflection layer. By taking advantage of the high light transmissivity of the material of the conversion layer, the possibility that light is absorbed by the Ohmic contact layer is reduced. The conversion according to the present invention can also block diffusion of the metal in the metal reflection to the p-type GaN. Accordingly, it can be used as both an Ohmic contact layer and a barrier layer.

The invention claimed is: 
     
       1. A light-emitting diode structure having a progressive work function layer, comprising:
 a semiconductor layer; 
 a conversion layer, disposed below said semiconductor layer; 
 a metal reflection layer, disposed below said conversion layer; 
 a bonding layer, disposed below said metal reflection layer; and 
 a substrate, disposed below said bonding layer; wherein said conversion layer comprises at least three sub-conversion layers stacked sequentially and with gradually decreasing work functions from top to bottom; 
 wherein the conversion layer comprises a plurality of dopants, and the number of said plurality of dopants decreases gradually from the interface between said conversion layer and said semiconductor layer to the interface between said conversion layer and said metal reflection layer. 
 
     
     
       2. The light-emitting diode structure of  claim 1 , wherein said semiconductor layer further comprises, from top to bottom, an n-type semiconductor layer, a multiple quantum well layer, and a p-type semiconductor layer stacked sequentially, and said conversion layer contacts said p-type semiconductor layer. 
     
     
       3. The light-emitting diode structure of  claim 2 , wherein the material of said p-type semiconductor layer is p-type gallium nitride. 
     
     
       4. The light-emitting diode structure of  claim 1 , wherein the material of said conversion layer is tin oxide. 
     
     
       5. The light-emitting diode structure of  claim 1 , wherein said plurality of dopants are aluminum nitride. 
     
     
       6. The light-emitting diode structure of  claim 1 , and further comprising a first electrode disposed on said semiconductor layer. 
     
     
       7. The light-emitting diode structure of  claim 1 , and further comprising a second electrode disposed on said semiconductor layer and exposed outside said bonding layer. 
     
     
       8. The light-emitting diode structure of  claim 1 , and further comprising a second electrode disposed below said substrate.